As known in the art, a certain shock absorber of a vehicle has a strut. One side of the strut is connected to a knuckle arm of one wheel of a front axle of a vehicle, and the other side is connected to a piston rod assembly combined with a chassis of the vehicle.
The strut has a seat in its upper part. The seat serves as a support surface for supporting a lower winding end of a suspension spring that internally houses the piston rod assembly. Therefore, the strut supports a front part of a vehicle along with the suspension spring. In addition, the strut is rotated with respect to an axial line of the shock absorber so as to allow for wheel steering. In particular, the strut is subjected to a strong mechanical action when a vehicle is in a braking operation, an acceleration operation, and a turning operation. For this reason, stiffness of the strut affects controllability of the wheel surface, so that a vehicle behavior on a road surface depends on this controllability.
The strut is required to be tolerable to various stresses in three spatial directions (e.g., vertical, horizontal, and longitudinal directions). Therefore, in general, the strut is manufactured in a monoblock manner and is formed of a metal material such as steel.